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Old 01-28-2011, 11:21 AM   #1
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Motorhomes, and Charging Batteries....

This all started with a dead house battery, and has evolved into a bunch of questions and ideas that is unique to us M/H owners, so I thought I would post it here and get some opinions and feedback.

Like most of us, I have:
A/ Engine battery X 1.
B/ House batteries X 2.

To charge those batteries I have:
1/ Engine Alternator.
2/ 120V AC to 12V DC Convertor(120v supplied via hookup or genset)

My plan is to add Golf cart 6V deep cycles, and a Solar panel/charge controller.
No problems there, however, in the course of the discussion over in the battery and univolt section, I ran into issues...

A bigger battery bank needs a good charger...
Ok, I thought, so the solar charger I like has the good stuff (MPPT controller).
Then I find out that I also need a a new Intelligent charger/converter because it seems nobody makes a battery charger/converter that can take power from both inputs, ie, solar and 120v.
So I have to double up on chargers?

Then we got into the alternator issue...
When driving, the engine alternator charges both engine and house batteries..
Now, most of us have a 105 or 140A unit, and asking that to charge an engine battery AND run the chassis stuff like lights, HVAC, and maybe engine fans is about the maximum.
Asking it to charge a bank of house batteries I think would be too much!

Now, I was thinking...

I live in Sunny Souther California, and as I do not have 120V access at my storage, so I want the solar panels/charge controller to keep the house batteries in a tiptop, ready to go state. While I am driving and using house power during daylight, the solar panels with be charging. I have enough capacity in my battery bank(600AH plus) to carry me thru the night, and the solars will recharge during the day again.
Lets not get too deep into how big my battery bank is vs usage and available wattage from the solar panels etc...

What if I relieve the alternator of the duty of charging house batteries?
Do I need it?
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Old 01-28-2011, 02:58 PM   #2
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Alternator question ?

is the 105 and 140 interchangeable ? plug in ready for either ?
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Old 01-28-2011, 05:00 PM   #3
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John, I have seen "OEM" sized Alternators rebuilt up to 180A, and when looking on Ebay, find them up to 250A.
This one I saw is rated at 105A at idle and 220A at 1200rpm!
NEW HIGH OUTPUT ALTERNATOR CHEVY 220 AMP ONE WIRE 65-85 - eBay (item 260616315960 end time Feb-02-11 19:23:31 PST)

Now, I do not know how this would work, and what mods would be needed beyond a beefed up charge cable, or if reliabilty would be a concern.
The output of 220A sounds great!

This one is a "One wire" unit, and I do know that my 345 has some kind of voltage regulator mounted on the radiator top... which sounds REALLY silly to me!
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Old 01-28-2011, 05:46 PM   #4
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My MH has a battery isolater. It keeps the engine battery charged 1st. Only when it has a full charge does it charge the 2 house batteries. I only have the 105 A alternator. The only time I see the alt. putting out a mega charge is when driving at night. There are a lot of exterior lights on a 345. Been experimenting with LED's but have'nt found the right combination yet.

Ricky
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Old 01-28-2011, 06:24 PM   #5
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Yep, I am sure mine only has a 105 too, and as you say, there are a lot of lights to run. Add a warm climb with house a/c on, and engine fans kicking in, and you are running a negative, let alone asking for the house batteries to get a charge!
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Old 01-29-2011, 12:45 AM   #6
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Originally Posted by 3 Dog Nite View Post
My MH has a battery isolater. It keeps the engine battery charged 1st. Only when it has a full charge does it charge the 2 house batteries. I only have the 105 A alternator. The only time I see the alt. putting out a mega charge is when driving at night. There are a lot of exterior lights on a 345. Been experimenting with LED's but have'nt found the right combination yet.

Ricky
I'm not an expert by any means but I thought the isolator allowed both groups of batteries to be charged from a single source, the alternator, but prevented either group, house or engine, from discharging the other.

To Keyair's origional question my 280 has the same battery set-up, 2 house and 1 engine battery. I also have the original Univolt that I rarely use because of the tendency of boiling batteries. I believe I have the same exterior lighting as the 34.5 and maybe 1 or 2 fewer interior lights. I do store at home but I do not leave it plugged in because I don't use the Univolt. I do have the diesel and I don't remember the alternator output but I don't recall it being unusually high, as a guess 90 or 105 amps.

We have been on several 3 and 4 day camp-outs and rallies. We essentially just dry camp. I do not hook up to the park water system. The water pump works fine. We can run 4 days on the tanks and then refill the tanks. I don't like the idea of the constant pressure on the old system. If something blows you fill the coach up with water. Same with the holding tanks, when full, I dump and put the hose away. If there is power I will plug in to use an electric heater and occasionally the microwave. The wife does use a curling iron and hair dryer. When we leave the alternator recharges the batteries with no problem. The engine batteries don't go down and most of the charge goes right to the house bank. Again I don't use the Unvolt and never show less than 3/4 charge on the monitor.

I don't know how far you travel to go camping but I travel at least 100 miles or more and never found the need to use auxiliary chargers. Maybe you don't travel as far or use more 12V accessories but so far I just don't see the need.

Cheers, Dan
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Old 01-29-2011, 08:47 AM   #7
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Isolator

[QUOTE=Smartstream;944320]I'm not an expert by any means but I thought the isolator allowed both groups of batteries to be charged from a single source, the alternator, but prevented either group, house or engine, from discharging the other.

Cheers, Dan[/QUOTE]

Dan
You are correct. The standard 3 wire diode Isolator will charge 2 battery banks from one generator source. You have no manual control, and I believe the Isolator will charge the lowest battery first. Again, the batteries should be the same type and approx. age for good results. (yes anything will work for a while, but may cost a lot over time)
The diode style isolator also has a voltage drop across the isolator, which may not be suitable for proper AGM battery charging.

A standard single isolator will not charge the chassis battery from shore power that charges the house battery, without some type of modification.
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Old 01-29-2011, 10:24 AM   #8
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Isolator, Separator

More info on this subject from this link.
Smith Auto Electric - Sure Power Industries

"The difference in whether to use a battery isolator or battery separator will depend on whether your alternator has internal or external voltage sensing. Many of the newer alternators are internal sensing and so cannot be used with an isolator, because of the loss of approximately 1 volt across the diodes, In these cases you would use a battery separator."

Dave
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Old 03-05-2011, 05:09 PM   #9
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Originally Posted by Keyair View Post
Then I find out that I also need a a new Intelligent charger/converter because it seems nobody makes a battery charger/converter that can take power from both inputs, ie, solar and 120v.
So I have to double up on chargers?
Yes, and that's not necessarily a bad thing. Not if, but when one fails the other is still usable. I have a Truecharge 40 for 120V and a Blue Sky 2000E for solar with about 350 watts of solar panels.

Quote:

Then we got into the alternator issue...
When driving, the engine alternator charges both engine and house batteries..
Now, most of us have a 105 or 140A unit, and asking that to charge an engine battery AND run the chassis stuff like lights, HVAC, and maybe engine fans is about the maximum.
Asking it to charge a bank of house batteries I think would be too much!
Mine is a 310 with a very rugged alternator supplied with the Isuzu ... but it's only 80 amps. I was concerned with that too and wired an option so the engine fans (which draw almost 20 amps) could run off either the chassis or house batteries.
Quote:
Now, I was thinking...

I live in Sunny Souther California, and as I do not have 120V access at my storage, so I want the solar panels/charge controller to keep the house batteries in a tiptop, ready to go state. While I am driving and using house power during daylight, the solar panels with be charging. I have enough capacity in my battery bank(600AH plus) to carry me thru the night, and the solars will recharge during the day again.
Lets not get too deep into how big my battery bank is vs usage and available wattage from the solar panels etc...

What if I relieve the alternator of the duty of charging house batteries?
Do I need it?
I don't think you do, but it doesn't matter. Leave the isolator for use when the solar is offline. The MPPT controller will deliver its set voltage to the house batteries, so the only time any current will flow from the engine alternator is when it (after the isolator diode) is producing a higher voltage -- as in when the solar or 120 is not working.

There is a lot of hooey in advertising about battery isolators. The purpose is to deliver charging current to two battery banks while preventing house loads from draining the chassis battery (and vice versa) when the engine isn't running. Isolators are made in several different versions. The simplest use two diodes. Originally they were plain silicon power diodes with a voltage drop of about 0.7 to 1.0 volts (substantially more at high currents in some cases due to poor choice of wire etc in assembly). Newer ones use low forward-drop diodes that lose 0.2 to 0.3 volts, or MOSFETs which can have slightly less drop. There is another way of doing this without diodes, which is to use a high current relay -- no drop at all if the contacts are in good shape. A "battery separator" is just a relay that automatically connects the two batteries together under certain conditions -- maybe this is better than triggering the relay manually, maybe it isn't.

If the alternator is heavily loaded with lights, fans etc. it won't be producing enough voltage to deliver any current to the battery anyway unless the battery is deeply discharged, so there is another reason not to worry.

It is a good idea to be sure that your voltage regulator sense line samples the voltage after the isolator, but in my view not essential. Many automotive alternators are set too high, to compensate for voltage drop in the wire. They often can't be adjusted and delivering 14.8 to 15.5 volts at nominal engine speeds. You really don't want this unless you need to recover a lot of charge very quickly. Losing a volt in the isolator is not the end of the world.

People seem very concerned about the boxes they choose, but then don't put the same energy into planning the installation. You need high quality crimped lug connectors, fat wire and suitable anti-corrosion grease to assure solid connections after years of use. UL-listed crimp lugs from T&B or Burndy are good, and No-Ox-Id A or A-special grease. A suitable hydraulic crimper with hex dies is really needed, but this is no longer an $800 project, the $70 one from Harbor Freight works fine up to about #2 AWG (ignore the gauge markings on the dies -- I don't know what they were thinking, maybe wire size instead of lug size.)
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Old 03-05-2011, 06:59 PM   #10
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I think you need the alternator it is unlikely you will always have full sun.
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Old 10-11-2011, 10:00 PM   #11
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Steve, did you ever decide what to do about your charging situation? Solar? New alternator? Or just waiting till you get out on the road for your camping trips to see what's really necessary?
Thanks, Derek
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Old 10-11-2011, 11:18 PM   #12
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Of my 2 House batteries which are older marine deep cycle, one already died, so I need to upgrade.

I am planning 4 x 6v Golfcart Batteries, with the mods I will do to the Battery storage, I can fit 6 easy, or 8 at a push, but then I am worried about weight..
Will need new charger to suit.

Solar is in my plan, but not a priority yet aside from maybe one panel to charge/top off the bank while waiting between trips.
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Old 10-12-2011, 08:01 AM   #13
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All very interesting, but electric is my weak point. My 345 also has 2 coach deep cycle and 1 chassie battery. The chassie does not charge when attached to shore power. All charge with gen or alt from engine. Is there an easy solution to charging all including the chassie battery when attached to shore power? I believe the wiring is original to the unit. Also note chassie battery will discharge when attached to shore power if not disconected by the wall solinoid. Have not found the drain point as yet.
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Old 10-12-2011, 10:44 AM   #14
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All very interesting, but electric is my weak point. My 345 also has 2 coach deep cycle and 1 chassie battery. The chassie does not charge when attached to shore power. All charge with gen or alt from engine. Is there an easy solution to charging all including the chassie battery when attached to shore power? I believe the wiring is original to the unit. Also note chassie battery will discharge when attached to shore power if not disconected by the wall solinoid. Have not found the drain point as yet.
You are correct, the shore power converter does not charge the chassis battery. You would need an isolator like what there is on the engine alternator so that one battery does not discharge the other.

I believe in simple solutions...I bought a $30 battery charger from Sears and I plug it in when I'm hooked to shore power.
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